Cutting styrofoam with a CNC machine and turning it into aluminum

One of the most popular ways of turning an object trapped inside the world of a computer into a real, metal object is the art of lost wax, or lost foam casting. In this process, a full-scale model of the object to be made in metal is crafted in either foam or wax, placed in a pile of sand, and burned away by molten metal.

[ptflea] over at the Bamberg, Germany hackerspace Backspace came up with a very clever build that automatically cuts foam into the desired shape, ready to be taken out to the backyard foundry. The build is based around an old flatbed scanner and a hot wire cutter. The old scanner conveniently had an equal number of steps per axis, so attaching an Adafruit motor shield and replacing the old control electronics was just an issue of finding the correct resistors.

Making stuff out of styrofoam is cool and all, but the real goal for this project was setting things on fire and melting old heatsinks. The styrofoam molds were placed in a bucket full of sand, and the furnace – a few ytong bricks, a crucible, and a propane burner – started to melt some aluminum. The molten aluminum was poured onto the mold and after cooling, the makers of Backspace had a few very cool aluminum trinkets.

A nice build that is able to produce some very nice metal objects. We suspect, though, that a higher-density foam (something along the lines of blue or green insulation sheets, if they have those in Germany) could produce an even higher level of detail if you’d like to build your own.

The styrofoam piece (core) is embedded in molding sand (=sand + additives that make it stick together). Then the liquid metal is poured into the mold via a canal; the styrofoam burns in the process.
Other techniques create a two part mold and the core is removed before the actual casting (because it is made out of a material which will not burn away like styrofoam).
Finally a wax model of your object can be covered with sand and ceramic which creates some kind of shell, the whole thing is then placed in a furnace which hardens the shell and melts the wax. The result is a hollow mold which can be filled with molten metal and can be easily broken after molding to retrieve the metal object.

It was just fine quartz sand without any additives. In fact it was so fine you can see the small balls from the styrofoam. We had a jar with the quartz sand and the styrofoam piece in it. A tip of this piece was outside so we could fill the aluminum in.
Styrofoam is 99,…% air and only a small part plastic, so it burns nearly without any debris when it makes contact with the around 700°C hot aluminium (=1292°F).
Here you can see the progress stepp by stepp:

Those insulation sheets are composite materials, they have solid layers separating the foam layers, this could be a problem for the casting process. Obviously denser foam means more plastic that needs to be burnt out.